(1) Field of the Invention
The present invention relates generally to an apparatus for cleaning sludge and other particles from heat exchanger surfaces and, more particularly, to a fluid discharge lance head of the type that is used for cleaning the heat exchanger surfaces of steam generators, e.g., nuclear steam generators.
(2) Description of the Prior Art
Steam generators, such as are found in nuclear power stations, generate steam used to drive turbines by heating water with heat exchangers. These heat exchangers are comprised of bundles of tubes with a heated liquid flowing therethrough. Steam is generated by water contacting the outer surfaces of the heat exchangers. The high temperatures and severe operating conditions incurred during steam generation cause sludge and other particles to accumulate on the surfaces of the heat exchangers, reducing heat transfer efficiency. Therefore, it is the practice to periodically remove accumulated deposits.
Sludge removal is normally effected using a device known as a lance connected to a source of pressurized fluid, e.g., water, steam or a gas. The lance may be permanently located in the generator, but is usually inserted through an opening is the generator wall when the heat exchanger surfaces are to be cleaned, and removed after cleaning.
The lance is normally comprised of a main tubular section or conduit having an inner end connected to a source of pressurized liquid, and a distal end that is closed. At least one, and generally a plurality, of nozzles or openings are located in the conduit wall between the inner and distal ends of the conduit for the purpose of discharging jets of liquid from the conduit interior into the steam generator and against the surfaces of the heat exchangers. Impact of the liquid, as a result of its physical force, normally removes a large percentage of the particles from the heat exchanger surfaces.
In some instances, however, the removal efficiency is less than desired, particularly when the position of the heat exchanger surfaces prevent the lance nozzles from being placed close to the surfaces. This lower efficiency is due to the fact that the force of the cleaning liquid decreases dramatically over even distances of a few inches. It has been recognized in the prior art that this loss in force, or jet decay, is primarily attributable to turbulence of the fluid exiting the lance nozzle.
Various attempts have been made in the prior art to reduce this turbulence, i.e., to produce discharge streams that are more laminar in nature, by different designs of the lance, and in particular the lance nozzle configuration. For example, U.S. Pat. Nos. 5,230,306 to Barringer et al; 5,241,723 to Garrabrant; and 5,505,163 to Jameel, all describe lance nozzle constructions that are said to improve the coherence and force of the discharge jet. The structures described in these patents, however, still do not provide optimum force.
Thus, there remains a need for a new and improved lance which improves the flow characteristics of the fluid being discharged from the lance onto heat exchanger surfaces in a steam generator while, at the same time, is simple to construct and use.